How the cake serving calculator works
Scaling a cake recipe starts with one number: the scale factor, which is the servings you need divided by the servings the recipe was written for.
Scale factor = target servings ÷ original servings
If a cake serves 8 and you need to serve 20, the scale factor is 20 ÷ 8 = 2.5×. You then multiply each standard ingredient by 2.5. Two cups of flour becomes 5 cups, 200 g of sugar becomes 500 g, three eggs becomes 7.5 (round to 7 or 8). The calculator does this multiplication for any one ingredient at a time and shows the factor so you can apply it to the rest of the list.
What scales linearly
Most ingredients scale directly by the factor: flour, sugar, butter, oil, milk, water, eggs, cocoa, and most extracts and flavorings. If you double the recipe, you double these. Because eggs come in whole units, round to the nearest whole egg (or weigh eggs in grams — a large egg is about 50 g without shell — for tighter control).
What doesn't scale linearly
- Leavening (baking powder, baking soda, yeast): use roughly 75–80% of the linear amount when scaling up. A batter that's twice as big doesn't need twice the gas — too much leavening makes the crumb rise fast, over-expand, and then collapse in the center. This calculator applies 78% to the amount above the original when the factor is greater than 1.
- Salt and strong spices: start at 50–75% of the linearly scaled amount and adjust to taste. The palate reacts to concentration, not to how big the batch is, so a straight multiply often oversalts a large cake. This calculator uses 65% for the increment above the original.
- Cook time: does NOT scale with the factor. Doubling the batter does not double the bake time — heat penetrates by the depth of the batter in the pan, not its total mass. A deeper or wider pan bakes longer; the same batter split across more pans bakes about the same. Judge doneness with a thermometer (most cakes are done at 205–210°F / 96–99°C in the center) or a clean toothpick, not the clock.
Watch your pan size
Scaling ingredients only works if the batter has somewhere to go. A single 8-inch round holds roughly 4 cups of batter; scaling to 2.5× gives about 10 cups, which needs a larger pan, an extra pan, or a taller cake tin. Fill pans no more than about two-thirds full so the cake has room to rise without spilling.